1. Field of the Invention
The present invention relates to body closure panels suitable for use on motor vehicles, and more particularly to a tailgate for pickup trucks.
2. Description of the Background
A conventional tailgate, as presently used in pickup trucks and other motor vehicles, may be a relatively heavy assembly, weighing up to about 50 pounds. The assembly is typically made from a number of stamped steel sheets that are joined together by resistance spot welding and hemming. Steel reinforcements may be welded to the sheets, adding strength and rigidity at critical locations.
Pickup trucks, as an example, are hard working vehicles wherein the tailgate is expected to perform reliably for many years. Pickup truck buyers expect that these closure panels be strong, reliable, and look good. The tailgates should also be manufactured to a close tolerance or margin, and all such manufactured tailgates should appear to have a uniform gap to adjacent panels. Tailgates are expected to withstand people or heavy loads standing on them in an open position, as well as loads placed on a top edge when they are closed. The tailgate assemblies may also be used to tie down payloads carried in the truck bed.
Because many pickup truck users are female and may be petite in stature, the tailgate is preferably as lightweight as possible while maintaining sufficient strength. It may also be desirable to reduce tailgate weight so that the truck""s payload can be increased without sacrificing fuel economy.
Presently available tailgates are heavy because they are made from steel. In addition, because they are assembled from many components, conventional tailgates may not be as reliable, strong, or durable as desired. These steel panels are also subject to attack by moisture, road salt, and other chemical agents in the environment that are corrosive to steel and eventually detract from its structural integrity and appearance. Accordingly, there is a consistent need to provide a lightweight, strong, durable tailgate panel for pickup trucks that has minimal impact upon vehicle cost. It is also desirable to reduce tailgate weight in order to improve fuel efficiency and truck payload capacity.
Some issued patents disclosing pickup truck tailgates include U.S. Pat. Nos. 4,861,093; 4,939,828; 5,328,225; 5,425,564; and 5,678,876. Although prior art pickup truck tailgates generally perform adequately, tailgates made from steel sheets detract from fuel economy and are cumbersome to lift manually because of their large weight. Accordingly, a lightweight replacement for steel is always desired.
In recent years, some vehicle body panels have been made from thermoplastic polymers. Such panels are often lighter than steel. However, they generally provide reduced strength and rigidity compared with steel panels. Because the tailgate has high strength expectations, these polymer-based body panels may not be appropriate in tailgate design.
As a possible partial solution to this strength versus weight problem, it has been suggested that a hybrid tailgate design, utilizing both lightweight plastics and metals, be implemented. For example, U.S. Pat. No. 5,944,373 (which is expressly incorporated by reference into this application in its entirety) discloses a hybrid tailgate assembly comprised of a plastic reinforcing module housed between a single metal sheet wrapped around the reinforcing module. The metal sheet may be made of an aluminum alloy to reduce the weight of the tailgate as compared to traditional steel tailgates. However, the tailgate may be more expensive and difficult to produce than traditional steel tailgates. Also, because the aluminum or other metal may not be as accurately formed as steel, many of these aluminum-based hybrid tailgate assemblies may not have acceptable mechanical tolerances or margins that meet customer expectations.
The hybrid tailgate works on the premise of an I-beam. A central member, or web, keeps apart two flanges located at opposite ends of the central web. The strength of the I-beam is determined, among other factors, from the strength of the two exterior flanges and their cross-sectional area. The interior central web separates the two flanges but can be weaker than the flange material (e.g., as with corrugated cardboard). Therefore, the hybrid tailgate uses the relatively weaker plastic material for the interior reinforcing module and the somewhat stronger aluminum or other material for the inner and outer panels (the flanges). An aluminum skin by itself, in the same configuration as the conventional steel tailgate, may not be stiff enough for the intended uses of the tailgate.
Even with the improvements over the prior art discussed above, there is a consistent need to further reduce the weight of the tailgate while preferably maintaining the strength and outward appearance of the tailgate. The tailgate may be made as a hybrid of plastics and metals, such as aluminum, and the tailgate assembly should be easy to manufacture as compared to conventional methods. Also, the resulting mechanical tolerances of the tailgate assembly once installed in a pickup truck or other motor vehicle are preferably improved in relation to the prior art.
These and other objectives and advantages of the present invention will become readily apparent to persons skilled in the art from the following description of particularly preferred embodiments.
In accordance with the present invention, there is provided a lightweight tailgate assembly for pickup trucks or other motor vehicles. The tailgate assembly includes inner and outer metal panels and a plastic reinforcing module attached between the inner and outer panels. The metal panels preferably act as a shell or housing around the reinforcing module.
In one aspect of the present invention, the metal panels may be made from aluminum or other sheet metal and preferably comprise an aluminum alloy of the AA2000, 5000, 6000 or 7000 series. Aluminum alloys of the AA6000 series, comprising aluminum alloyed with magnesium and silicon, are particularly preferred. The metal panels are preferably made from a single sheet, stamped and folded into a desired configuration.
The tailgate assembly may also include top and bottom metal panels extending between the inner and outer panels. The top and bottom panels are preferably generally parallel to each other. The inner and outer panels are also generally parallel.
The reinforcing module may comprise a thermoplastic resin, preferably polyester reinforced with glass fibers. Other suitable thermoplastics include polyolefins such as polypropylene and ethylene-propylene copolymers, polyvinyl chloride, polycarbonates, polyurethanes, and mixtures thereof. The reinforcing module preferably provides separation and support to the metal outer shell.
The reinforcing module includes a main leg extending between side legs; a top leg adjacent the top panel; a plurality of support legs connecting the main leg and the top leg; and two bottom legs extending diagonally downwardly from the main leg to lower portions of the side legs. Preferably, the reinforcing module includes side legs of sufficient geometry to at least partially constitute the side panels of the completed tailgate. This may reduce the necessity of heavier metal side panels.
The fastener used to attach the metal panels to the reinforcing module may include metal screws or bolts such as a plurality of metal screws extending through the metal inner panel into the reinforcing module. In a preferred embodiment, the reinforcing module can be connected with the metal inner and outer panels by an adhesive, either in addition to or in place of the screws.
In a preferred embodiment, the tailgate assembly includes a hinge device (hinge collar) for connecting the assembly to a truck body. A preferred hinge device may be a plastic hinge collar that is integrally molded into the reinforcing module. Alternatively, the tailgate assembly may include separate metal hinge collars attached to the plastic side panels and extending laterally outwardly. The metal collars mate with metal hinge pillars or pins attached to rear corner posts on the truck body.
Two such collars are placed collinearly in the horizontal plane at the lower portion of the tailgate for a conventionally-opening (top-down) tailgate. Similarly, two collars are placed collinearly with an axis in the vertical plane for at least one embodiment of a side-swinging tailgate. In either case, the collars may be integrally molded into the reinforcing module or may be separate metal hinge collars.
The tailgate assembly also includes a latch assembly for locking the tailgate between opposed rear corner posts in a truck body. The latch assembly includes a base plate attached to the inner panel; a handle supported by the base plate and extending through an opening in the outer panel; and connecting rods extending laterally outwardly from the handle and connecting with the rear corner posts. For a side-swinging tailgate, the latch preferably engages with the rear corner posts only on the side of the tailgate opposite the vertical hinges described above.
If some users do not wish to have visible plastic side legs on the tailgate, optional cover plates may be attached to the outside of the plastic side legs to at least partially obscure the plastic edge. These cover plates may include the metal hinge collars described above. These and other embodiments and advantages of the present invention will be better understood with reference to the following figures and detailed description.